Now that Monster Energy Drinks and 5-Hour Energy have everyone's attention, the FDA is figuring out its next move: how to investigate the drinks, and how to regulate them.

A new letter sent from the FDA to Senator Richard Durbin of Illinois shows new explanations from the FDA as to how it will approach the 18 deaths and 150 injury reports linked to energy drinks, The New York Times reports. The FDA revealed that it may seek outside help from experts to determine whether the drinks are safe or not. That may include a review from the Institute of Medicine of the National Academy of Sciences.

The letter stated that caffeine intake has generally remained stable, despite the recent popularity of energy drinks — and that caffeine isn't necessarily unhealthy. "Although these products have the potential to raise safety or regulatory issues, there is a long history of safe use of other caffeine containing products in the United States," the letter states.

The letter also shed light on the stimulants in energy drinks — including taurine and guarana, two ingredients that have caused controversy in the past for their safety. In short, certain ingredients are exempt from FDA pre-market approval if they are considered to be generally recognized as safe. "With respect to taurine and guarana... FDA searched the literature but did not find any information that calls into question the safety of these ingredients as currently used in beverages. Thus, to date, FDA has made no deterination with respect to the intended technical effects of their use in 'energy drinks,' which may include both flavoring and stimalating effects," the letter reads.